Reinforced concrete slab resting on soft ground

ABSTRACT

A reinforced concrete slab formed to provide a rugged support when resting on soft soil to form a runway for aircraft or the like, said slab being formed of reinforced concrete and provided with reinforced concrete projections shaped to form pockets for the reception of soil, said projections being resistant to bending and being secured rigidly to the underside of the slab.

United States Patent Inventor Radan M. Sedijatmo Djakarta, IndonesiaAppl. No. 841,521 Filed July 14,1969 Patented June 29, 1971 AssigneeN.V. lntraport Amsterdam Amsterdam, Netherlands Priority June 17, 1965Netherlands 6507747 Continuation-impart of application Ser. No. 556,731,June 10, 1966, now abandoned.

REINFORCED CONCRETE SLAB RESTING ON SOFT GROUND t ne PrimaryExaminer-Jacob L. Nackenoff Attorneys-John P. Chandler and Snyder andButrum ABSTRACT: A reinforced concrete slab formed to provide a ruggedsupport when resting on soft soil to form a runway for aircraft or thelike, said slab being formed of reinforced concrete and provided withreinforced concrete projections shaped to form pockets for the receptionof soil, said projections being resistant to bending and being securedrigidly to the underside ofthe slab.

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OOOOQO INVEI JTOR REINFORCED CONCRETE SLAB WESTIING ON SOFT GROUND Thisapplication is a continuationin-part of US. application Ser. No. 556,731filed June 10, 1966 now abandoned.

This invention relates to a reinforced concrete slab formed to provide arugged support when resting on soil to form a roadway for vehicles, arunway for aircraft or a foundation for a machine or building.

The construction of runways for aircraft in poor or soft soils alwaysrequires a considerable amount of earthmoving firstly for excavation ofthe soft soil to the depth of 1.5 to 2.0 meters, depending upon theaircraft loading, secondly for the transportation of the excavated softsoil, and thirdly for the arrival of sand to replace the excavated softsoil.

The layer of sand beneath the actual runway is of a thickness of 1.50 to2.0 meters and serves to distribute the wheel pressures of the aircraftover such a large area of the soft soil beneath the layer of sand thatthe permissible pressure on the soil-which is of the order of 0.2 to 0.3kgJcm. is not exceeded. To satisfy this requirement, the layer of sandhas to be kept dry by means ofa good drainage system.

The earthmoving requires a considerable amount of heavy equipment, sothat first of all the required access roads have to be constructed overthe said poor soils. After the required soil stabilization and sandfilling have been provided an extensive and good system of drainagepipes is fitted to keep the sand course dry. The construction of theactual runway cannot start until this has been done, and the runwayconsists of a hard course about 0.50 meters thick ofsand and rock with asurfacing of about 30 cm. cement concrete. The said thicknesses of thecourses depend upon the maximum aircraft load.

It will be apparent that the said operations require a con siderableamount of material transport. The object of the invention isconsiderably to reduce the costs for material transport and constructiontime by completely eliminating all the preparatory and associated work,such as soil stabilization by means of sand filling and the constructionof an extensive and good drainage system to keep the sand course dry. Tothis end, the invention provides a reinforced concrete slab formed toprovide a rugged support when resting on soft soil to form a runway foraircraft or the like, said slab being formed of reinforced concrete andprovided with reinforced concrete projections shaped to form pockets forthe reception of soil, said projections being resistant to bending andbeing secured rigidly to the underside of the slab, said slab having athickness of the order 8 to 25 centimeters, said projections having awidth of about I to 2 meters and a length of about 1 to meters and beingspaced apart about L2 to 4 meters.

According to the invention, the function of the said sand course istaken over completely by a relatively thin slab of reinforced concreteprovided with an efficient stiffening system formed by the projections,so that the relatively thin slab of reinforced concrete, which can be 8to cm. thick, can properly carry out its pressure-distributing function.This stiffening system is distinguished by its simple form andcomposition, and also by the simplicity and convenience ofitsconstruction. This simplicity and convenience of construction are at amaximum in soft soils where the soil water level is high.

The quantity of concrete to be used for constructing a slab according tothe invention is small. This small quantity can be decreased by applyingprojections deriving their stiffness in all vertical planessubstantially from their form.

The projections preferably consist of tubes.

It is advantageous for the projections to extend to a greater depth atthe edges of the slab than the projections at the center thereof.

The invention also provides a method for constructing a slab accordingto the invention. This method is characterized by the followingsuccessive steps:

inserting prefabricated projections in the soil and pouring a layer ofreinforced concrete over said projections. The lefabricated projectionscan easily be inserted even in very soft soil, particularly in morass.

The projections may consist of prefabricated round tubes of reinforcedconcrete. The outside diameter, length and spacing will depend upon thenature of the soft soil and the maximum loading expected on the slab,which will be explained in the following description with reference tothe accompanying drawing, wherein:

FIG. I is a top plan view of part of a runway according to theinvention.

FIG. 2 is a cross section on the line lI-II in FIG. ll.

FIGS. 3a3fdiagrammatically illustrate a number of examples of crosssections and formations of projections of other slabs according to theinvention.

FIG. 4 shows diagrammatically a plan view of a slab according to theinvention.

FIG. Sis a side view ofthe slab according to FIG. 4 and FIG. 6 is a sideview on larger scale of the part V of FIG. 5.

When it is required to construct a runway in an area where the firm soil1 has an overlying course of soft or poor soil 2, for example of acompressive strength of 0.2 to 0.3 kg./cm. prefabricated reinforcedconcrete tubes 3 are recessed into the soft soil 2. Each tube 3 isrecessed into the soil as follows: the soil within the upright tube isfirst excavated in layers either manually or mechanically. As theexcavation of the soil advances, the tube is advanced into the soiluntil the required depth has been reached. The excavated soil, whichduring excavation was temporarily piled around the circumference of thetube, is then completely returned to the original plane inside the tubeand tamped down well until the tube is completely embedded rigidly andimmovably in. the ground to the depth shown in FIG. 2. In some cases,for example in very soft soil, the relatively lightweight and shorttubes can easily be driven into the ground,

Once all the tubes 3 have been fitted, the steel reinforcement of theslab 4 is twisted in known manner and the concrete is then poured as foran ordinary floor slab. It must be expressly pointed out that care mustbe taken to ensure a rigid and immovable connection between the slab andthe tube so as to prevent any angular turning between the tube and theslab, To this end, the reinforcing wires of the tubes can project at thetop, form the prefabricated concrete and act as anchors or hooks in theslab 4. The top edges of the tubes 3 may also project somewhat above thesoil in these tubes.

No drainage system whatever is required in the ground, since the slab 4is adapted to transmit the wheel pressure of the heaviest aircraft tothe subsoil in its natural state over an adequately wide area.

The tubes 3 are not intended to transmit the wheel pressures of theaircraft on the slab to the firm soil via the tubes as is the case withwell foundations. In actual fact the tubes 3 are as it were suspended inthe soft soil from the slab 4. No further explanation is necessary toshow that this new method of applying stiffened reinforced concreteslabs to soft soilsparticularly when the water level is high-can becarried out much more simply and quickly than in the conventional mannerusing main and bridging joists of reinforced concrete. The stiffeningaction of the tubes 3 on the slab 4 is due to the fact that when thesoil beneath the slab is loaded it is so compressed by the tubes that itcannot escape laterally, so that the slab remains stiff as it were.

The above-described runway or road has the very important advantage thatit requires no reinforcing or stiffening for increasing wheel loads,since the heavier wheel pressure simply has to be transmitted by thesame slab over a larger area to the soft soil while with conventionalrunways and roads a complete reinforcement or thickening of thepressure'distributing sand course and of the roadway itself isnecessary.

Although round tubes are preferably, square or other tubes havingangular cross sections can be used as projections.

The invention also covers slabs for which the projections are not formedby tubes. FIG. 3 shows a number of examples of cross sections offormations of such projections.

The projections derive their stiffness substantially from their formpreferably not only in one vertical plane, like the projections of FIG.3e but in all vertical planes, like the projections of FIGS. 3a. 3b. 3aand 3f and particularly like the pro jections'ofFlGS. l and 2.

' FIG. 6 shows the part Vl ofthe slab of FIG. 5.

The dimensions of the slab according to the invention. which areindicated in FIG, 6 are for example as listed in examples l and ii. inexamples I and ll the security factor n=l .5. However. the dimensionsmay be calculated with a security factor 12 resulting in smallerprojections 3 or with a security factor 2.0 resulting in largerprojections 3.

in this example the pitch distance between two adjacent projections =0.

The load is for example an equally distributed load p.

The height of the projections h.

i The width of the projections b.

The specific weight of the soil together with the ground water possiblyfound therein c.

The internal friction angle of the soil concerned 1 EXAMPLES i Thesecurity factor n=l .5 The pitch distance a of adjacent projections 2 m.The width b ofthe projections 1.2 m.

The security factor n=l .5. The pitch distance a=2.5 m.

The Width of projections b=l .5 m.

C rp p h specific weight friction specific height of soil angle of loadof projec- (ton/mfi) soil (ton/m!) tions (rn.)

2 2. 5 2. 82 1.3 1O 3 3. O 3. 5 3. 16 2 {I i 2. 5 2 3 2. 90 3. 5 3. Of!2 2. 34 2. 5 2. 5O j a 2.67 3. 6 2. 82

WALL THICKNESS In these examples I and ll the wall thicknesses of thetubes are so computed. that they are rigid enough to withstand bendingload.

in the above examples I and ii the wall thickness w of the tubes 8 cm.

SLAB THICKNESS d in the above examples I and ll a slab thickness of d=l0a l2 cm. is required. This slab has such a small thickness owing to thefact that the span length between two adjacent projections which isequal to pitch distance a is so small.

EXAMPLE ill The security factor n=l l.

The specific loadp is l ton/m The specific weight of the soil (=2. l.The internal friction angle of the soil d =25. The pitch distance 11 4m. and the length li=l m.

EXAMPLE IV The security factor n=2.0.

The specific load p is 5 ton/mi The specific weight of the soil c=l .7.

The internal friction angle of the soil 1 =9A. The distance a=l .5 rn.and the width IF] .2 in.

EXAMPLE v The security factor n=l .l

The specific load p is 1 ton/ml.

The specific weight of the soil c=2.l

The internal friction angle ofthe soil 1 25". The slab thickness d=25cm.

The width b=l m.

EXAMPLE VI The security factor n=2.0.

The specific load p=5 ton/mi The specific weight of the soil c=l .7.

The internal friction angle of the soil 9 10.

The length li=5 m. and the width b==2 in.

As the slab according to the invention is practically stiff the slab canbe loaded by a point load P which is equal to the product ofthe specificload 2 and the slab area RL.

What l claim is:

l. A reinforced concrete slab formed to provide a rugged support whenresting on soft soil to form a runway for aircraft or the like, saidslab being formed of reinforced concrete and provided with reinforcedconcrete projections shaped to form pockets for the reception of soil,said projections being resistant to bending and being secured rigidly tothe underside of the slab. said slab having a thickness of the order 8to 25 centimeters, said projections having a width of about 1 to 2meters and a length of about l to 5 meters and being spaced apart about1.2 to 4 meters.

2. Slab according to claim 1, characterized in that the projections areof tubular configuration.

3. Slab according to claim 1, wherein said reinforced concreteprojections have reinforcing wires projecting therefrom which areimbedded in the concrete slab.

4. Slab according to claim 1 characterized in that the projections inthe middle of the slab are shorter than the projections situated nearerthe edges of the slab.

5. A reinforced slab as claimed in claim 1 wherein the slab thicknesswithin the projections of tubular configuration is greater than the slabthickness between said projections.

6. A reinforced concrete slab formed to provide a rugged support whenresting on soft soil to form a runway for aircraft or the like, saidslab being formed of reinforced concrete and provided with reinforcedconcrete projections shaped to form pockets for the reception of soil,said projections being resistant to bending and being secured rigidly tothe underside of the slab, said slab having a thickness of the order 15to 20 centimeters, said projections having a width of about 1 to 1.5meters and a length of about 1 to 3 meters and being spaced apart about2 to 3 meters.

7. Slab according to claim 6. characterized in that the projections areoftubular configuration.

8. Slab according to claim 6. wherein said reinforced concreteprojections have reinforcing wires projecting therefrom which areimbedded in the concrete slab.

1. A reinforced concrete slab formed to provide a rugged support whenresting on soft soil to form a runway for aircraft or the like, saidslab being formed of reinforced concrete and provided with reinforcedconcrete projections shaped to form pockets for the reception of soil,said projections being resistant to bending and being secured rigidly tothe underside of the slab, said slab having a thickness of the order 8to 25 centimeters, said projections having a width of about 1 to 2meters and a length of about 1 to 5 meters and being spaced apart about1.2 to 4 meters.
 2. Slab according to claim 1, characterized in that theprojections are of tubular configuration.
 3. Slab according to claim 1,wherein said reinforced concrete projections have reinforcing wiresprojecting therefrom which are imbedded in the concrete slab.
 4. Slabaccording to claim 1 characterized in that the projections in the middleof the slab are shorter than the projections situated nearer the edgesof the slab.
 5. A reinforced slab as claimed in claim 1 wherein the slabthickness within the projections of tubular configuration is greaterthan the slab thickness between said projections.
 6. A reinforcedconcrete slab formed to provide a rugged support when resting on softsoil to form a runway for aircraft or the like, said slab being formedof reinforced concrete and provided with reinforced concrete projectionsshaped to form pockets for the reception of soil, said projections beingresistant to bending and being secured rigidly to the underside of theslab, said slab having a thickness of the order 15 to 20 centimeters,said projections having a width of about 1 to 1.5 meters and a length ofabout 1 to 3 meters and being spaced apart about 2 to 3 meters.
 7. Slabaccording to claim 6, characterized in that the projections are oftubular configuration.
 8. Slab according to claim 6, wherein saidreinforced concrete projections have reinforcing wires projectingtherefrom which are imbedded in the concrete slab.
 9. Slab according toclaim 6, characterized in that the projections in the middle of the slabare shorter than the projections situated nearer the edges of the slab.